Sheet binding

ABSTRACT

Sheet binding where the printing medium itself is the sheet binder. In a xerographic process, high density areas of the toner are provided at desired binding areas. These toner binding areas may then be subsequently refused between adjacent overlaying sheets to provide bound sacks without requiring any separate or additional binding materials.

Feb. 26; 1974 I G PIfAlLLlE SHEET BINDING 3 Sheets-Sheet 1 Filed Aug.25, 1972 G. P. TAILLIE Feb. 26, 1974 SHEET BINDING 3 Sheets-Sheet 2Filed Aug. 25, 1972 G. P. TAILLIE SHEET BINDING Feb. 26, 1974 5Sheets-Sheet Filed Aug. 25, 1972 United States Patent 3,794,550 SHEETBINDING Gordon P. Taillie, Rochester, N.Y., assignor to Standard OilCompany, Chicago, Ill. Filed Aug. 25, 1972, Ser. No. 283,676

Int. Cl. B32b 3/00, 7/14 U.S. Cl. 161-147 18 Claims ABSTRACT OF THEDISCLOSURE Sheet binding Where the printing medium itself is the sheetbinder. In a xerographic process, high density areas of the toner areprovided at desired binding areas. These toner binding areas may then besubsequently refused between adjacent overlaying sheets to provide boundstacks without requiring any separate or additional bind ing materials.

Copending application, Ser. No. 298,980, filed Oct. 19, 19 72, by RodgerH. Eichorn, with the same assignee, claims subject matter disclosed butnot claimed, herein.

The present invention relates to a very simple and economical method ofbinding two or more indicia bearing sheets together by providing on thesheets additional minor high density areas of the same indicia impartingmaterial in areas of desired binding, where the sheets are subsequentlystacked and the additional indicia imparting material commonly fusedbetween adjacent sheets at the binding areas to fasten the sheetstogether.

Sheet binding is one of the oldest known arts, and numerous methods andapparatus are known in the art for permanently or temporarily securingsheets together. Many of these, of course, are only economically suitedfor high priced or high volume commercial printing operations. There isa long standing need for improved sheet fastening means for localized,simple, and inexpensive binding of, for example, stacks of two to fiftypages.

This need has been greatly increased by the widespread use ofxerographic equipment, where large numbers of printed sheets areproduced by relatively unskilled personnel in non-commercial printingoperations. The demand for simplicity and economy in these applicationshas continued to retain conventional metal staples as the primaryfastening means. This is in spite of the fact that stapling, riveting orother sheet binding means requiring penetration of the sheet createsstress points in the sheets which encourage sheet tearing andinadvertent sheet removal. So does any sharp edges on the staples orrivets. Further, the pull-off strength of the top and bottom sheets inany stack fastened in this conventional manner is limited by thestrength of the sheet over only the small areas directly underlying theheads of the staple or rivet.

Thus, it is clear that a sheet binding method which provides inter-sheetadhesion over a much larger binding area than staples or rivets, andwhich does not require any sheet penetration or sharp edges, is greatlypreferable. Various adhesive bonding methods have been developed whichhave suitable binding strengths but they have not achieved widespreadutilization in many low volume binding applications, apparently becausethey are not sufficiently simple and economical in comparision to metalstaples or rivets. They require the supplying, handling and containmentof separate adhesive materials, and require separate adhesiveapplication steps in addition to the normal indicia printing steps.Examples from the adhesive binding are shown in U.S. Pats. Nos.2,579,488; 2,830,706; 2,898,973; 3,026,228 and 3,502,532. Some of theseutilize chemicals similar to those found in xerographic toners, but theyare not toners or inks. Other examples of adhesive sheet welding withheat and/or pressure, by pre-coating the sheet with clear plastics orice other separate binding materials, are discussed in the September197d issue of Book Production Industry, pp. 53-55, which discussses U.S.Pat. No. 3,560,290.

It has been known that in certain situations xerographic toners becometacky, softened or liquified. U..S. Pats. Nos. 2,638,416; 2,788,288;2,917,460; 3,053,688; 3,262,806; 3,268,332 and 3,488,189 are examples ofpatents noting these toner characteristics. These characteristics areconventionally utilized for fixing the desired indicia onto individualsheets. Or they may be used for transferring images from one web toanother, as in strip out imaging processes, e.g. U.S. Pat. No.3,275,436. However, printing inks and toners are carefully selected andprepared to avoid and prevent any inter copy sheet adhesion as soon aspossible after the copy sheet printing is accomplished, because thiswould seriously interfere with normal printing operations and isconsidered highly disadvantageous in the art. Thus, toners or printinginks are not considered in the art as adhesives, and, in fact,inter-sheet adhesive properties are carefully avoided by or tonerformulators.

In spite of, and contrary to the teachings of the art, the presentinvention teaches that a secure inter-sheet binding may be achievedutilizing only the conventional and commercially available printingindicia itself as the sole sheet binding agent, rather than adhesives orother separate bindings. Fusible xerographic toners have been found tobe particularly suitable. By the term fusible (as used herein inconnection with the indicia imparting material, such as xerographictoner) is meant a material which in its normal ambient state isnon-adhesive (nontacky), but is rendered sufliciently tacky for sheetadherence temporarily by heat or solvent vapors or pressure or somecombination thereof. The desired toner material here is one that isrefusible, i.e. easily rendered adhesive at least a second time, at anytime after its initial fusing. Some examples of fusible and refusiblexerographic toner compositions are disclosed in U.S. Pats. Nos.3,609,082; 3,577,345; 3,590,000 and Re. 25,136. Suitable refusiblexerographic toners are commercially available world-wide from the XeroxCorporation and its subsidiaries, and are already present in theirexisting xerographic copying and duplicating machines.

The method and article of sheet binding disclosed herein overcomes thestructural disadvantages of metal rivets and other penetrating bindingsdiscussed above. It provides strong and sheet tear-resistant bindingshaving a larger binding area. The method of the invention enables theuse of existing ink or toner supply, dispensing and sheet applicatingapparatus already available in the printing appara tus, and withoutrequiring any modifications or additional processing in the printingoperations. The only additional step required for the present process isa simple and noncritical refusing operation which can be preformed atany time in conjunction with, or subsequent to, the indicia printingoperation, and in any location. This refusing may be accomplished byvarious inexpensive and simple or commercially available apparatus. Forexample, the stack to be bound may be simply clamped at the binding areabetween a pair of heated pressure platens. Thus, it may be seen that thepresent process is particularly suitable for local sheet binding inofiices or other existing xerographic machine locations.

The exemplary embodiment described hereinbelow discloses theincorporation of the process of the invention in an otherwiseconventional exemplary xerographic process and apparatus. Accordingly,said processes and apparatus need not be described in detail herein,since various printed publications and patents and publicly usedmachines are available which teach details of various suitable exemplaryelectrophotographic and xerographic structures, ma-

terials and functions to those skilled in the art. Some eX- amples aredisclosed in the books Electrophotography by R. M. Schaffert, andXerography and Related Processes by John H. Dessauer and Harold E.Clark, both first published in 1965 by Focal Press Ltd., London,England, and the numerous patents and other references cited in thesebooks. All of these references are hereby incorporated by reference inthe specification. Also incorporated by reference herein are the abovecited references from the adhesive binding art, for their showings ofvarious sheet assembling, clamping and heating apparatus which may beutilized in the final steps of the present process. Accordingly, thepresent specification is specific to those details of the embodimentwhich represent a departure from the prior art, and further desireddetailed description will be provided by the above references.

Further objects, features and advantages of the present inventionpertain to the particular steps and details where by the above-mentionedaspects of the invention are attained. Accordingly, the invention willbe better understood by reference to the following description and tothe drawings forming a part thereof, which are substantially to scale,wherein:

FIG. 1 is a perspective view of a document of bound sheets in accordancewith the present invention;

FIG. 2is a magnified cross-sectional partial view of the binding areataken along the line 2-2 of FIG. 1;

FIG. 3 is a perspective view of a transparent overlay with an opticalmask, retaining an original as shown, for producing binding areas inxerographic copies of the original in accordance with the presentinyention;

FIG. 4 is a cross-sectional simplified plan view of an otherwiseconventional xerographic machine showing severl modifications which canbe provided thereon for producing the process of the invention;

FIG. 5 is an enlarged top view of an optical mask which may be utilizedin the apparatus of FIG. 4;

FIG. 6 is a perspective view of an exemplary refusing apparatus for theprocess of the invention, shown with an exemplary stack of sheetsinserted therein; and

FIG. 7 is a simplified top view of the principal operating componentswithin the apparatus of FIG. 6.

Referring to the drawings, there is shown in FIGS. 3-7 some examples ofapparatus for performing the sheet binding processes of the invention.It will be appreciated that various steps of the process can also beperformed manually or by other apparatus, including that disclosed inthe previously cited references.

FIGS. 1 and 2 show one example of a completed article of manufacture inaccordance with the present invention. Specifically there is shown asecurely edge bound stack 10 of individual paper sheets 12. The sheets12 are bound only at a binding area 14. This binding area 14 extends ina stripe along, or closely adjacent to, the entire left hand edge of allof the sheets 12 in the stack 10. This stripe is wider thanapproximately 5 millimeters. The binding areas are preferably located atthe same position on each of the sheets 12, so that with the sheets 12aligned overlying one another, the binding areas 14 are also so aligned.Each binding areas 14 is substantially continuously covered and occupiedby a corresponding high density area 16 of fusible xerographic toner 18.Preferably each sheet 12 has at least one such high density areas 16.The toner 18 of this high density area 16 is the same toner 18 asprovides the indicia 20 on the sheets 12, and it is preferably providedin the same step and at the same time as the imaging of the indica 20.

As may be seen particularly from the magnified crosssectional view ofFIG. 2, the inter-sheet binding consists solely of the high densityareas 16 of toner 18 being commonly fused between immediately adjacentsheets 12 at the binding area 14. It may be seen that the toner 18,which was initially prefused into the binding areas of the individualsheet 12, is additionally refused into the sheet immediately above orbelow it, The n r is refused into all of the sheet surfaces in the caseof conventional porous paper, as shown, to form a strong interlockingbond.

The strength of the inter-sheet bond is a function of the area, density,and degree of fusing of the xerographic toner between adjacent sheets.By increasing these parameters the inter-sheet bond can be madesubstantially stronger than the tear resistance of the sheet materialitself. Correspondingly however, by reducing one or more of theseparameters in the binding process there can be provided an inter-sheetbond which is sufficient to normally retain the sheets together, but yetwhich allows removal of individual sheets without sheet tearing, i.e., apad type of binding can be provided wherein one or more sheets can bepulled off the stack neatly, with the separation occurring at therespective inter-sheet toner bond.

It will also be noted that the stack 10 may be additionally bound byconventional staples, rivets or other mechanical fastening means, asshown by exemplary staple 22 in FIG. 1. If done in the binding areas,this provides a binding which is far stronger than such conventionalmechanical binding means can provide in themselves. This is because whensuch mechanical fasteners penetrate the sheets in the stack only withinthe fused binding areas, they are not limited by their normal stressconcentrations and small area sheet strength limitations. The stack areaaround the area of fastener penetration is bonded together andreinforced by the refused toner and strongly resists sheet tearing as aunit. These advantages similarly apply if apertures through the sheetsare desired at the binding areas for ring binding or the like. It willbe appreciated that combinations with mechanical fastenings means arenot required and that the present process can provide suflicient bindingstrength to be the sole binding means for permanent binding.

The binding area 14 of FIGS. 1 and 2 is a contiguous single edge bindingarea. However, it will be appreciated that the binding area may be inonly one corner of the sheets, for example, or there may be severalseparate binding areasrather than a single one.

Referring to FIG. 4, there is shown therein by way of example, one typeof conventional xerographic apparatus. The process of the invention maybe performed thereon utilizing this apparatus in its conventional modeof operation. Thus, an indicia bearing original 23 here isconventionally optically imaged onto a charged photoreceptor surface 26to form an electrostatic image of said indicia thereon. Thiselectrostatic indicia image is conventionally developed by attracting anelectrostatica'lly attractable and fusible xerographic toner 18 to saidelectrostatic image which attracted toner 18 is then fused onto thedesired copy sheets 12. (As is well known, in certain other types ofxerographic processes using photosensitive treated paper, the chargedphotoreceptor is integral the copy sheet.) The fusing of all of thetoner 18 onto the copy sheet is accomplished by a conventional fusingoperation 30 in the xerographic apparatus. The completed image copysheets 12 are then deposited at the output in a catch tray 32 or othersuitable sheet receptor which provides assembly of the copy sheets in anoverlying stacked uniform relationship.

Considering now FIGS. 3-5, there are illustrated thereon examples ofdifferences in otherwise conventional xerographic sheet processing whichenable the sheet binding process of the invention to be accomplished.They are merely exemplary, and numerous other means will be apparent tothose skilled in the art. FIG. 3, illustrates an optical mask 34 whichfunctions as an overlay to the indicia bearing original during imagingin the apparatus of FIG. 4, or other xerographic apparatus. The opticalmask 34 is here provided by an opaque area 36 on an otherwise fullytransparent clear plastic jacket 38, into which the original 24 issimply inserted. The opaque area 36' corresponds in proportion, size,location and area to the desired binding area 14 on the copy sheet.(With a one-t -one reduction it will be identical.) i

The opaque area 36 is located on the side of the jacket 38 which isbetween the original and the photoreceptor, i.e., in the optical paththerebetween. Thus, in the xerographic imaging process there is therebyformed an in tense additional electrostatic charge image on the minorarea of the photoreceptor which corresponds to the desired binding areaon the copy sheet. This additional image is in addition to theelectrostatic indicia image, and is formed at the same time and by thesame ap paratus. Accordingly, in the same operation in which toner 18 isattracted to the electrostatic indica image, the high density area 16 oftoner is attracted to the additional minor image area and additionallyimparted to the copy sheet at the binding area 14. This additional tonerarea is fused along with the indicia in the conventional fusingoperation 30. The optical mask 34 is preferably dimensioned so as toprovide a high density area 16 of toner on the copy sheet of thedimensions previously discussed.

FIGS. 4 and 5 illustrate a different type of optical masking operationto achieve the same result of forming the high density area 16 of tonerat the binding area 14. This optical mask 40 is shown in an enlarged topview in FIG. 5, and in position in a side view in FIG. 4. The exemplarymask 40 is a plate reciprocally movable in and out of the optical pathbetween the original 24 and the photoreceptor at one edge thereof. Whenso inserted, it functions in the same manner as described above for theoptical mask 34. It may be inserted manually or by an automaticapparatus such as the electrical solenoid 42 shown.

It has been additionally found that both the optical masks 34 and 40,while preferably substantially fully opaque, are preferably finelyoptically apertured. That is, they are preferably made up of amultiplicity of small opaque areas separated by small transparent spacesin between. In the case of a desired binding area 14 in the form of astripe or band as illustrated, the optical mask is preferably made up ofa multiplicity of closely spaced opaque lines. Preferably these linesare approximately .05 to 5 millimeters (.002 to V8 inch) wide and arespaced apart by approximately .05 millimeter (.002 to .003 inch orslightly greater), whereas as previously discussed, the entire band ispreferably wider than approximately 5 millimeters inch). The providingof an optical mask in this configuration takes advantage of, andutilizes for the purpose of the invention, the phenomenon of edgedevelopment in electrophotography. This phenomenon per se is welldiscussed in the previously cited text references and accordingly neednot be discussed herein. The result of a mask of this aperturedconfiguration with edge development is a much higher toner concentrationover what would otherwise be the interior of solid areas. Thus, muchhigher overall toner density is provided in the desired binding areasthan would be provided by a solid area mask. Closely spaced dots ratherthan lines may also be used for the same purpose. Cross-hatching hasproven effective.

An alternative method by which the desired optical mask may be providedin the path between the original and the photoreceptor is to simplypreprint a dark area on the original. As a further alternative, the copysheets themselves may be preprinted with sufficient toner in the desiredbinding areas. These methods of course require an additional step unlesspreprinting is required for other reasons.

Another way of forming the additional electrostatic image needed toprovide the high density toner binding area or areas is furtherillustrated in the apparatus of FIG. 4. An exemplary additional corotron44 or. other suitable charging apparatus is shown adjacent thephotoreceptor in the path of the photoreceptor after its initial chargehas been received. By briefly applying a voltage to this additionalcorotron 44, an additional electrostatic image may be formedelectrically (non-optically) by electrically changing the charge on theselected minor additional area of the charged photoreceptor. Thismethod, of course, requires more apparatus than the simple optical masksdescribed above. However, this apparatus is well known and available inthe art.

Considering next the exemplary ways in which the high density bindingareas 14 of toner 18 on the individual sheets 12 are bound together toform an integral stack 10, as previously described the sheets areassembled together in a directly overlying relationship in a position inwhich they are to be bound. It is not essential that all of the bindingareas directly overlie one another although this is preferable. At thecatch tray 32 of FIG. 4 there is provided an exemplary pair of pressureplatens or dies 46 and 48 located at the lower end of the catch traywhere one edge of the sheets commonly abuts a stack stop. They comprisehere one fixed heated platen 46 and one movable heated platen 48,located respectively at opposite sides of the stack 10. The platens 46and 48 provide refusing for binding between adjacent sheets by heatingthe stack at the binding area 14 sufiicient to render the high tonerdensity area 16 on the sheets (only at the binding areas) sufficientlytacky to adhere between adjacent sheets, while simultaneously pressingthe binding areas 14 together under pressure between the platens 46 and48. The platen 48 is moved with pressure down against the top on thestack. This pressure is suificient to remove air spaces between thesheets at the binding areas, and to provide good inter-sheet tonertransfer, including improving the flow of toner from its carrier sheetinto the adjacent sheet surface. The heating is continued until thetoner on at least one sheet is softened sufiiciently to adhere to thenext adjacent sheet for each of the number of sheets being bound.Preferably, the stack 10 is further held between the dies for a timeperiod after the heating is terminated sufiiciently to allow the tonerto substantially re-solidify by cooling.

The platens 46 and 48 are shown here with schematic representations ofconventional electrical heating coils in the platen surfaces to providethe refusing heat. However, it will be appreciated that numerous otherfusing means and processes may be utilized including those described inthe above-cited references.

While, as described above, all of the sheets to be bound in a singlestack may be first assembled together and bound simultaneously in asingle binding/refusing step, other variations are possible. For examplethe refusing process may be repeated for each individual sheet to bebound. One way this may be accomplished is for the binding area of theuppermost sheet in the stack to be radiant heated to maintain the tonertherein sufficiently adhesive, the next sheet for the stack to beindividually placed on the stack with a binding area contacting thestack, and this single additional sheet to be bound to the stack bydownward movement of the platen in synchronism with the addition of thesheet. By repeating this step for each additional sheet, as manyadditional sheets as are desired may be bound to the same stack Withoutrequiring heating of the entire stack. correspondingly, or incombination, individual sheets may be added and bound to the stack oneat a time by rendering or maintaining the toner area on the added sheetsufficiently tacky during the time that it is added to the stack andclamped by the platen thereon. A thermal shield 50 extending from thefusing operation 30 down over the catch tray 32 is illustrated here byway of an example for effecting the latter step by maintaining the tonerarea 16 warm and tacky from the original fusing operation 30 for thebrief time needed to place it over the stack and press it down thereon.

FIGS. 6 and 7 illustrate the exterior and interior details respectivelyof a further exemplary apparatus 52 for performing the final refusingstep for binding described above. As may be seen from FIG. 6, theapparatus 52 is designed to accept the stack 10 of sheets 12 verticallydownwardly therein and to align the lower edges thereof for binding as asingle bound stack. As may be seen from FIG. 7 this may be accomplishedby a relatively simple apparatus 52 comprising a stationary platen 54operated against by an opposing moving platen 56. The moving platen 56is driven under pressure to compress together the binding areas 14 ofthe stack by a rotatably driven cam 58. The cam 58 causes a cam follower59 to reciprocate, and it in turn moves the moving platen 56 throughcoil compression springs 60. The springs 60 restrict the amount of forcewhich can be applied to the moving platen 56, and thereby preventjamming of the machine. However, an increased thickness of the stack 10will cause greater compression of the springs 60 and therefore a desiredgreater compression force to be applied to the stack. Electrical heatingelements as shown may also be provided here to heat the platens.Additional heating means can also be provided in the bottom surfaceagainst which the stack abuts. The above described apparatus 52 is forthe purpose of providing the application of both heat and pressure forstack binding. It will be appreciated that depending on the type ofxerographic toner selected, that pressure alone may be sufficient, orthat vapor or other known fusing methods may be provided. It will alsobe appreciated that numerous other apparatus may be utilized, such aspressure dies in the form of continuous rollers, etc. Further, pressurecan be, but need not necessarily be, applied before, while, or after thetoner is heated.

Any type of original image indicia may be utilized with the presentprocess, Whether hard copy, microfilm, microfiche, graphic, or alphanumeric, since the binding process does not interfere in any way withthe normal indicia imaging or printing except at the selected bindingareas. Likewise, almost any copy paper may be utilized. For example, thepresent process may be utilized to provide bound demand-printed papercopies of microfilm reports, texts or the like. It is especiallysuitable for direct on-line binding of pre-collated output sets fromhigh speed machines.

For microfilm or other reversal image input, it will be appreciated thatan opaque image mask will not be suitable. In this case the additionalimage area for toner binding can be provided by additional light sourcesimaged through apertures corresponding to the above-described masks. Theabove-described method utilizing the corotron 44 or the like can also beused.

It will also be noted that either one or both of the immediatelyadjacent (overlying) binding areas may have the prefused toner binderareas thereon. If both adjacent surfaces have high density toner areas16, this will give an even stronger bond since more binding toner 18 isavailable in the intersheet space, and also since deeper tonerpenetration of both sheets may have been provided in the original fusingin this manner.

It will also be noted that in situations where there is not an estheticproblem, that it is possible with the present process to print orindicia a number of additional unused binding areas in addition to thebinding area which may eventually be utilized. In fact, by printingbinding areas on all copies produced, whether intending them to be boundor not, subsequent binding together of any of the sheets may be readilyaccomplished at any time by completion of only the refusing step of theabove-disclosed process. The black binding areas which would be exposedon the unbound copies would not be objectionable in many situations,since they would occupy only a small area of the sheet margin outside ofthe normal indicia-occupying area. Thus for convenience, it is alsopossible to completely mask both edges of the original so as to providea substantial toner area along both edges of the copy sheets. Only theone edge which is clamped and subjected to refusing will be a bindingarea. There is no binding etfectby these further high density areas oftoner,

since if they are not refused in the refusing step, they will not bindthe sheets together.

Providing binding areas at both sheet edges may be particularlydesirable in the case of duplex or pseudoduplex copying where thedesired binding areas may be at alternating sides of the respectivesheets. In pseudoduplex output format, where two sheet folds or materialare bound together at every other fold line to provide the individualduplex pages, it may be desirable to place the binding areas on bothsides of both edges of each sheet.

In situations where the esthetic factor of exposed black toner areas isa problem, it will be noted that all the binding areas which are boundare not visible except for binding areas exposed on the upper orlowermost sheets of the stack. These can be eliminated simply byinsuring that the upper and lowermost sheets to be bound only havebinding areas facing the stack.

Several stacks 10 can be simultaneously bound by a modification of theprocess herein. A large common assemblage of all the sheets for severalstacks can be formed, interspersed with one or more sheets having noadjacent inter-sheet binding areas thereon. These interspersed sheetsare located between the desired individual bound stacks. The entireassemblage can then be subjected to the toner refusing step. Theinterspering sheets will prevent inter-sheet binding to themselves, butnot interfere with the binding together of all of the other sheets withtoner binding areas. Thus, in a single binding operation, several boundstacks can be simultaneously produced without adhering to one another.Note that these interspersed non-binding sheets can be provided by thelast sheet of one stack and the first sheet of the next stack having nobinding areas on their outward facing surfaces, which is also desirableesthetically. This elimination of binding areas on selected sheetsurfaces can be provided automatically, for example, by programmedactuation of the solenoid 42 to remove the imaging light mask 40 forpreselected sheets.

Note that the term sheet as used in the specification and claims hereinis defined (conventionally) as including both individual cut sheets andalso sheet segments of continuous web or fan fold or accordian foldpaper or the like, whether burst or unburst. The subject method isapplicable to those machines in which the paper is roll fed and is cutor folded into its individual sheets only after the toner has beenapplied and first fused into the binding areas.

In conclusion, it may be seen that there has been disclosed herein anovel and improved sheet binding method, and a bound stack producedtherefrom, having numerous advantages in both simplicity, economy, andfasten ing security. The exemplary embodiments described herein arepresently considered to be preferred; however, it is contemplated thatfurther variations and modifications with the purview of those skilledin the art can be made herein. The following claims are intended tocover all such variations and modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. A method of binding two or more indicia bearing sheets togethercomprising the steps of applying fusible indicia imparting material tosaid sheets for indicia purposes;

applying an additional high density area of the same fusible indiciaimparting material to the same said sheets respectively at at least oneselected minor desired binding area of said sheets;

then assembling two or more of said sheets in an overlying relationship,and

while said sheets are so assembled, fusing said indicia material betweensaid adjacent sheets only at said selected binding areas sufficiently toachieve intersheet binding by said high density areas of said indiciaimparting material being commonly fused between adjacent sheets at saidbinding areas.

9 2. The method of claim 1 wherein said additional high density area isapplied simultaneously with said indicia imparting material and by thesame process.

3. The method of claim 1 wherein said selected binding area is a smallarea at an edge of each of said sheets having substantially the samerelative location and area on each sheet.

4. The method of claim 1 wherein said indicia imparting material isfusible electrostatically attractable toner and wherein said highdensity area thereof is imparted with said same toner in the same step5. The method of claim 4 wherein said high density area is imparted byinserting an optical mask over the desired high density areas in theindicia imparting process.

6. The method of claim 4 wherein said high density area is formed byelectrostatically attracting toner to the binding area on said sheetswith an electrical charge separately and specifically applied to saidsheets for that purpose.

7. The article of manufacture comprising:

a bound stack of overlying adjacent sheets xerographically imaged byfusible xerographic toner pre-fused therein;

said sheets having additional high density areas of the same xerographictoner pre-fused into at least one minor binding area thereon; and

said binding consisting solely of said high density areas of xerographictoner being commonly fused between immediately adjacent sheets at saidbinding area.

8. In the process wherein an indicia is imageable onto a charged surfaceto form an electrostatic image of said indicia thereon, and wherein thiselectrostatic indicia image is developable by attracting anelectrostatically attactable and fusible toner to said electrostaticimage, which attracted toner is then fusible onto the desired copysheet; the improvement comprising the steps of:

forming an intense electrostatic charge image on at least one selectedminor area of said surface; attracting a high density area of the samesaid fusible toner to said selected minor area;

fusing said high density toner area to said copy sheets at at least oneselected minor binding area of said sheets;

assembling two or more of said copy sheets in a stacked relationship;and

while said sheets are so assembled, re fusing said toner between saidadjacent sheets only at said binding areas sufficiently to achieveintersheet binding by commonly fusing said toner between adjacent sheetsonly at said binding areas.

9. The process of claim 8 wherein said process is xerographic, saidsurface is a photoreceptor and said electrostatic image is formablethereon by optically imaging through an optical path an indicia bearingoriginal thereon, and wherein said additional electrostatic image isformed simultaneously with the formation of a said'electrostatic indiciaimage b an optical mask inserted in a minor portion of the optical pathbetween said indicia bearing original and said photoreceptor.

10. The process of claim 9 wherein said optical mask is provided bypre-printing an area on the original corresponding to the desiredbinding area on the copy sheets.

11. The process of claim 8 wherein said additional electrostatic imageis formed electrically and non-optically by electrically changing thecharge on a selected minor area of said charged surface.

12. The process of claim 8 wherein said re-fusing comprises heating saidsheets at said binding areas until the toner on at least one sheet hassoftened sufiiciently to adhere to the next adjacent sheet, and pressingsaid binding areas of said sheets together under pressure between a pairof dies, said pressure being sufiicient to remove air spaces betweensaid sheets at said binding areas.

13. The process of claim 12 wherein said stack is further held betweensaid dies for a time period after said heating is terminated sutficientto allow said toner to substantially re-solidify by cooling.

14. The process of claim 8 wherein said stack is additionally bound byextending mechanical fastening means through said sheets in said stackonly within said re-fused binding areas.

15. The process of claim 8 wherein said re-fusing process is repeatedfor each individual sheet to be bound.

16. The process of claim 8 wherein said re-fusing process is performedonce simultaneously on all of the sheets to be bound together.

17. The process of claim 8 wherein said high density toner areas areapplied to both sides of said copy sheets.

18. The process of claim 8 wherein the top and bottom sheets of saidstack have said high density areas of toner applied only to the sidesthereof facing said stack.

References Cited UNITED STATES PATENTS 9/1972 Miller et al. 156l'51 7/1943 Gurwick 270-52 US. Cl. X.R.

' inn/7223b UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIQN PatentNo. 3,794,550 Dated February 26, 1974 Inventor(s) Gordon P 'I'ail'lie Itis certified that error appears in the above-idenflfied patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 1, top, change "Standard Oil Company, Chicago,

Illinois" to -Xerox Corporation, Stamford, Conn.

Signed and sealed this 15th day of Oc tober 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner ofPatents USCOMM-DC 60376-P69 u. s. covznmuzu-r PRINTING OFFICE muoass-3:u,

FORM PO-1050 (10-69)

